Imaging of osteochondral injuries.
Acute injuries can produce fragments consisting of cartilage alone or cartilage and underlying bone. A purely cartilaginous fragment creates no direct radiographic abnormalities, whereas one containing calcified cartilage and bone appears as a radiodensity. The advent and refinement of MR imaging have led to the detection of occult injuries of subchondral bone and cartilage that can escape identification on routine radiographic analysis. The available data appear to indicate a substantial role for MR imaging in the analysis of lesion stability in cases of osteochondritis dissecans; however, further studies are required to determine its advantages over other methods, in particular, arthroscopy. Indirect evidence of cartilage abnormality on MR images relates to the identification of fluid at the interface between the fragment and the parent bone. The MR imaging technique influences dramatically whether such fluid is identified. MR arthrography employing the intra-articular injection of gadolinium compounds can be advantageous in the delineation of the chondral surface and in the detection of intraarticular bodies. Optimally, MR imaging would allow direct analysis of the cartilage surface, and specific imaging sequences that are most suited to this analysis are still evolving.